The present invention relates to a valve apparatus for controlling hydraulic pressure of a hydraulic pressure operated actuator usable for a clutch or a brake, and a method for controlling hydraulic pressure.
A hydraulic pressure control apparatus applicable for a clutch, disclosed in Japanese Laid-Open Patent publication No. 235732/1988, will be explained as an example of prior arts.
FIG. 9 shows a clutch cylinder 101 and a control valve 102 for controlling the clutch cylinder 101 in the above prior art. The control valve 102 includes a pressure control valve 103 for controlling clutch hydraulic pressure, and a flow rate detection valve 104. The flow rate detection valve 104 is provided with a sensor section 105 for detecting filling and clutch pressure level. The pressure control valve 103, the flow rate detection valve 104 and the sensor section 105 are stored in an integrated housing (107 as shown in FIG. 10). The pressure control valve 103 and the sensor section 105 are electrically connected to a controller 106.
As shown in FIG. 10, the control valve 102 includes an input port 110, an output port 111 and drain ports 113 and 114. To the input port 110 of the control valve 102, a hydraulic fluid supply line delivered from a pump (not shown) is connected. And, to the tip of the output port 111, the clutch cylinder 101 (as shown in FIG. 9) is connected.
The pressure control valve 103 has a spool 115, the right end of which comes in contact with a plunger 117 of a proportional solenoid. In the left end of the spool 115, a piston 119 is installed and a spring 118 comes into contact with the spool 115. In the spool 115, a hydraulic chamber 120 close to the piston 119 and a hydraulic passage 121 communicated with the hydraulic chamber 120 are formed. Hydraulic pressure in the hydraulic passage 122 is applied, as a feedback pressure, to the hydraulic chamber 120 via a hydraulic passage 121.
The flow rate detection valve 104 has a spool 125, which defines hydraulic chambers 126, 127 and 128 in the housing 107. An orifice 130 is formed between the hydraulic chambers 127 and 128. Springs 131 and 132 abut on the left and right ends of the spool 125, respectively. The spool 125 is positioned at the neutral position as shown in FIG. 10 under a resilient force of the springs 131 and 132 when pressure dose not rise in the hydraulic chambers 127 and 128. When the piston 125 is at the neutral position, the hydraulic fluid, which has reached from the input port 110 to the flow rate detection valve 104 via the hydraulic passage 129, remains in the hydraulic chamber 126.
A detection pin 134 made of metal is disposed on the upper right side of the flow rate detection valve 104. The pin 134 detects that the spool 125 is displaced in the rightward direction from the neutral position, as shown in FIG. 10, overcoming a resilient force of the spring 132. The detecting pin 134 is mounted to the housing 107 by a cover 135 via an isolation sheet 136. From the end of the detecting pin 134, a lead wire 137 is extended, which is connected to a point xe2x80x9caxe2x80x9d located between resistances R1 and R2 which are connected to each other in series. Between the resistances R1 and R2, a predetermined magnitude of DC voltage V (for instance, 12 V) is applied. The end of the resistance R2 and the housing 107 are grounded respectively. The sensor section 105 comprises these spring 132, detecting pin 134, and resistances R1 and R2.
Next, operation of the hydraulic pressure control apparatus for a clutch having the above-mentioned structure will be explained referring to FIG. 9 to FIG. 11.
The horizontal axis shows a time t in FIG. 11(A) to FIG. 11(E). The vertical axis of FIG. 11(A) shows current I commanded from the controller 106, the vertical axis of FIG. 11(B) shows a pump pressure P0, the vertical axis of FIG. 11(C) shows hydraulic pressure (clutch pressure) P1 in the hydraulic chamber 127 in the front of the orifice 130, the vertical axis of FIG. 11(D) shows hydraulic pressure (clutch pressure) P2 in the hydraulic chamber 128 in the back of the orifice 130, and the vertical axis of FIG. 11(E) shows a output S (a voltage at a point xe2x80x9caxe2x80x9d) of the sensor section 105.
When a clutch is connected, at a time point t1 in FIG. 11, the controller 106 operates so that trigger command current 1I is supplied to the proportional solenoid 116 of the control valve 102. Thereafter, the controller 106 operates so that the trigger command current I1 is lowered to an initial pressure command current 10 and this condition is maintained until the termination of filling. The initial pressure command current 10 corresponds to an initial pressure Pa (as shown in FIG. 11(D)) of the clutch pressure.
By supplying the trigger command current I1, the spool 115 of the pressure control valve 103 is displaced in the leftward direction so that the input port 110 is communicated with the hydraulic passage 122. Consequentially, the hydraulic fluid delivered from the pump is introduced from the input port 110 into the hydraulic chamber 127 of the flow rate detecting valve 104 via the hydraulic passage 122, and then into the hydraulic chamber 128 via the orifice 130. At this moment, differential pressure (P1-P2) is generated between the hydraulic chambers 127 and 128 due to the existence of the orifice 130. The differential pressure causes the spool 125 to be displaced in the leftward direction, so that the flow rate detecting valve 104 is opened. Therefore, the hydraulic fluid flows from the input port 110 into the hydraulic chamber 127 via the hydraulic passage 129 and the hydraulic chamber 126, and then into the clutch via the orifice 130, the hydraulic chamber 128 and the output port 111. The hydraulic fluid continues to flow until a clutch-back becomes completely filled.
Here, when the spool 125 is positioned at the neutral position in FIG. 10, and, during a period in which the spool 125 is being displaced in the leftward direction from the neutral position, the spool 125 is parted away from the detecting pin 134. Accordingly, the potential at the point xe2x80x9caxe2x80x9d is a voltage Vxe2x80x2, which is obtained by dividing the voltage V by the resistances R1 and R2, as shown in FIG. 11(E).
When the clutch-back is completely filled with the hydraulic fluid, the filling is terminated. At this time, since the hydraulic fluid stops flowing, there is no difference in pressures at the front and back of the orifice 130 (that is, P1=P2). At this moment, the spool 125 is displaced in the rightward direction by the spring 131 and a difference in the pressure receiving areas of the spool 125 result in the detecting pin 134, once conducted to the housing 107, being grounded via the spool 125. The conduction is effected by displacement of the spool 125 due to shoot pressure generated at the termination of filling. And, the spool 125 returns to the neutral position in FIG. 10 when the shoot pressure disappears. Accordingly, as shown in FIG. 11(E), the potential at the point xe2x80x9caxe2x80x9d is lowered to zero at a time point t2, and rises to Vxe2x80x2 again. A detecting signal S showing the potential at the point xe2x80x9caxe2x80x9d is inputted to the controller 106, which determines the termination of filling from the potential rising at point xe2x80x9caxe2x80x9d. At the termination of filling, the controller 106 operates so that the command current I for the clutch cylinder 101 is gradually increased from the initial pressure command current 10 (as shown in FIG. 11(A)). Incidentally, the controller 106 operates so that the command current for a pre-stage clutch is lowered to zero at the determination of the termination of filling, as shown FIG. 11(A) with a dashed line.
As the result, the clutch pressure is lowered from the shoot pressure to the initial pressure Pa and then gradually increased as shown in FIG. 11(D). Accordingly, the spool 125 is displaced in the leftward direction from the neutral position. Thereafter, when the clutch pressure is gradually increased further to exceed a set pressure Th of the spring 132 at a certain time point t3, the spool 125 is displaced in the rightward direction again with the result that the right end of the spool 15 comes in contact with the detecting pin 134. Therefore, at the time point t3, the potential at the point xe2x80x9caxe2x80x9d is lowered to zero again, and thereafter maintained at that level.
So, the potential at the point xe2x80x9caxe2x80x9d becomes zero when the pressure in the clutch is higher than the set pressure Th, while the potential becomes a predetermined voltage when the pressure in the clutch is less than the set pressure. Accordingly, by monitoring the potential at the point xe2x80x9caxe2x80x9d, it is possible to know the presence or absence of the clutch pressure (that is, the engagement state of the clutch). And, in this case, since the potential at the point xe2x80x9caxe2x80x9d rises after once being lowered to zero, due to the shoot pressure generated at the termination of filling, it is possible to know the termination of filling by detecting the first rising of the shoot pressure.
However, the above-mentioned hydraulic pressure control apparatus for a clutch has following problems.
(1) Response of the flow rate detecting valve 104 is inferior. So, as shown in FIG. 11(D), at the termination of filling, considerable shoot pressure is generated, which may cause speed changing shock.
(2) The pressure control valve 103 is directly driven by thrust of the plunger 117 of the proportional solenoid 116. Thus, if the capacity of the solenoid 116 is small, the thrust may be small, whereby a mis-operation of the pressure control valve 103 may easily occur due to biting of particles in the pressure fluid. On the other hand, when a strong solenoid is employed, the sufficient thrust can be obtained, but causes an increase in cost.
In view of the above-mentioned problems, the object of the present invention is to provide a valve apparatus and a method for controlling hydraulic pressure of an actuator applicable for a clutch or brake, which has such advantages that a generation of peak pressure (shoot pressure) can be lowered, mis-operation due to biting of particles can be reduced, or the cost thereof can be reduced.
To solve the above-mentioned problems, the present invention provides a valve apparatus for controlling hydraulic pressure for a clutch or a brake comprising a pressure control valve (30) has a clutch or brake cylinder inner pressure feedback chamber (31x) at one end thereof and a pilot pressure receiving chamber (31y) at another end thereof. The pressure control valve introduces a clutch or brake engagement pressure hydraulic fluid, which has been brought to flow into a clutch or brake cylinder chamber, into the above-mentioned clutch or brake cylinder inner pressure feedback chamber (31x), and increasing the hydraulic fluid pressure of the clutch or brake engagement pressure hydraulic fluid to balance with a magnitude of pilot pressure that is generated in the pilot pressure receiving chamber (31y), so that the pressure control valve (30) controls the clutch or brake cylinder pressure. The valve apparatus also comprises a pilot fluid passage (19), through which the hydraulic fluid flows from a branched passage (18) having a throttle (26a) to the pilot pressure receiving chamber (31y) of the above-mentioned pressure control valve (30) and drains it into a tank. The valve apparatus further comprises a pressure proportional valve (50) which controls the pressure of the pilot fluid that has flowed into the above-mentioned pilot pressure receiving chamber (31y) by positioning a valve element (55) thereof at either position within a drain interruption position, a throttle drain position or a drain release position; a proportional solenoid (40), which changes the position of the valve element (55) of the above-mentioned pressure proportional valve (50) against the flowing of the pilot fluid, and controls the magnitude of the pilot fluid pressure. The valve apparatus also comprises and a pressure switch (60), which communicates with a output port (13) of the above-mentioned pressure control valve (30) and detects the clutch or brake initial engagement pressure when the clutch or brake cylinder hydraulic chamber will be filled with the hydraulic fluid.
Since the conventional flow rate detecting valve, which is relatively inferior in response, is eliminated, the peak pressure (the shoot pressure) at filling completion will not be generated. In addition, it is possible to reduce costs. In addition, since the control is carried out by the pilot pressure, even if the proportional solenoid has small capability, the opening size of the main passage formed at the main valve is large, whereby a large amount of hydraulic fluid can flow and an operation defect of the main valve due to biting of particles will be prevented.
In one aspect of the valve apparatus for controlling hydraulic pressure for a clutch or a brake according to the present invention, it is preferable that the pressure switch operates when the clutch or brake cylinder hydraulic chamber is filled with the hydraulic fluid, thereby rising the clutch or brake initial engagement hydraulic fluid pressure therein, and the pressure switch does not operate when the pressure in the clutch or brake cylinder hydraulic chamber is less than the initial engagement pressure.
In one aspect of the valve apparatus for controlling hydraulic pressure for a clutch or a brake according to the present invention, it is preferable that a filtering means h is provided upstream of the throttle (26a) mounted at the pilot fluid passage (19). In this aspect, particles can be removed by the filter thereby preventing the throttle passage from being blocked.
In addition, in one aspect of the valve apparatus for controlling hydraulic pressure for a clutch or a brake according to the present invention, it is preferable that a second filtering means (230) is provided outside of a casing upstream of the above-mentioned filtering means. In this aspect, replacement and cleaning of the filter can be easily carried out.
The method for controlling hydraulic pressure of the hydraulic fluid control valve, which employs the valve apparatus for controlling hydraulic fluid discussed above connected to a controller, comprises the following five steps.
The first step is for flowing a large amount of hydraulic fluid into the clutch or brake cylinder hydraulic fluid chamber just before the chamber is filled with it. In the step, a clutch or brake engagement start command is inputted to a controller, which operates to output a large amount inflow command current to the proportional solenoid of the hydraulic fluid pressure control valve for a predetermined period. As the result, the drain of the pilot fluid drained from the pressure proportional valve to a tank is interrupted and the pilot fluid pressure in the pilot pressure receiving chamber is increased to a high level, so that a communicating port between the input port and the output port of the pressure control. valve becomes large.
The second step is for flowing a small amount of hydraulic fluid into the clutch or brake cylinder hydraulic fluid chamber until the chamber is filled with it. In the step, after the predetermined period in which the large amount inflow command has been outputted, the controller operates to output a small amount inflow command current to the proportional solenoid of the hydraulic fluid pressure control valve. As the result, the pilot fluid is drained from the pressure proportional valve to a tank through a throttle and the pilot fluid pressure in the pilot pressure receiving chamber is lowered, so that the communicating port between the input port and the output port of the pressure control valve becomes small.
The third step is for detecting the termination of filling. In the step, when the clutch or brake cylinder hydraulic fluid chamber has been filled with the hydraulic fluid and the clutch or brake initial engagement pressure rises, the pressure sensor provided at the hydraulic fluid pressure control valve detects the rising of the clutch or brake initial engagement pressure and outputs this information to the controller.
The fourth step is for gradually-increasing the clutch or brake cylinder initial engagement hydraulic fluid pressure. In the step, the controller, which has been inputted information regarding the termination of filling, operates to stop outputting the small amount inflow command current to the proportional solenoid of the hydraulic pressure control valve and then supplies a gradually-increasing command current to the solenoid for a predetermined period, so that the clutch or brake initial engagement hydraulic fluid pressure reaches a set pressure for the predetermined period. As the result, the opening size of the throttle, through which the pilot fluid is drained from the pressure proportional valve to the tank, is gradually decreased to allow the pilot fluid pressure in the pilot pressure receiving chamber to be gradually increased, and the pressure in the clutch or brake cylinder inner pressure feedback chamber of the pressure control valve to be increased to balance with the gradually-increased pilot fluid pressure.
The fifth step is for outputting the set pressure command signal to the proportional solenoid of the hydraulic fluid pressure control valve. In the step, after the predetermined period in which the clutch or brake initial engagement hydraulic fluid pressure is being increased, the controller operates to stop the hydraulic fluid pressure gradually-increasing command current, and to keep the clutch or brake engagement set pressure, in which the gradual-increase of the pressure has been finished.